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Flashing led
1. Timer IC 555
This timer IC was introduced by Signetics corporation
of U.S. in the year 1972.
Features of IC NE555:
•Supply voltage range: D.C. 5 to 18V
•Current sinking and sourcing capacity: 200mA
•High temp. stability.
•Timing can be adjusted from microseconds to hours.
•Good timing stability against supply voltage
variations.
•Low cost.
•Versatile in operation.
6. Working
• Here, the IC is used as an astable multivibrator.
Thus the astable circuit will always keep
changing its state and the LED will keep flashing
without any external trigger.
• The LED will be “ON” when the capacitor C1 is
charging and will be “OFF” when it is
discharging.
• The capacitor charges through resistors R1 & R2
and discharges through resistor R2.
• Charging time is given by
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7. • Discharging time is given by
• The “ON” time & “OFF” time can be adjusted
by changing the values of R1,R2 & C1.
• Frequency of oscillations is given by
• Resistor R3 will limit the current through LED.
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